This invention generally relates to photosensitive polyurethane materials, more particularly to polyurethane solutions that are photosensitive or photopolymerizable when subjected to actinic radiation of the type that is utilized for exposing lithographic plates, photoresists and the like. The polyurethane photopolymers include recurring urethane groups, urea groups or combinations thereof in its backbone, and unsaturated hydrocarbon groups such as allyl groups are attached to the backbone, preferably through an ether linkage. Polyurethane photopolymers according to this invention are coated from a solvent system, and their molecular weight and viscosity are preferably controlled by selective reaction of a diamine with terminal --NCO groups.
Plates, especially those used for lithographic or planographic printing procedures, generally comprise a plate base or support member, a sub-base coating and a photosensitive coating. The plate base typically is a flexible sheet such as paper, metal, polymer film or the like which is treated, if necessary, with a suitable sub-base coating to provide a hydrophilic surface to which one or more photosensitive coatings are applied. Various plates, including lithographic printing plates, photoresists, and other articles having a substrate and one or more photosensitive layers thereover, have been devised over the years.
When the photosensitive layer is negative working, it becomes insolubilized upon imagewise exposure to actinic radiation. After such imagewise exposure, the plate is developed, whereupon the unexposed, unreacted portion of the imagewise exposed material is removed, and the hydrophilic sub-base material is uncovered at these locations. Since the exposed locations are insolubilized, they are not removed by the developer, and since they are oleophilic they readily receive and hold ink and readily transfer the ink as a printed image to a surface such as paper. The greater the abrasion resistance of the photosensitized material, the greater the number of times the ink can be transferred to the surface being printed, particularly in high-speed presses and the like that subject the developed plates to severe conditions.
Certain photopolymers are known to provide plates having enhanced abrasion resistance when compared with other, more sensitive materials such as diazonium compositions. Particularly important in the development of this technology is United States Letters Pat. No. 3,808,004, which discloses various photosensitive cinnamoylated photopolymer coatings which are especially suitable for use as a coating over a diazonium compound layer on a plate such as a lithographic plate or a photoresist for making printed circuit boards and the like. Photopolymers disclosed in that patent include a polyurethane cinnamate photopolymer for making presensitized, negative-working lithographic printing plates, such polyurethane resin having phenol blocking groups attached by a thermally unstable linkage that permits unblocking when desired.
One particular advantage of polyurethane materials is that they are especially abrasion resistant because they are both tough and flexible. Many polyurethanes, however, are unsuitable as photopolymers on a commercial scale because they possess virtually no or very limited photoreactivity properties or have a photospeed that is slower than desired for many applications.
Typically, a plate that has especially high abrasion resistance, such as one including a polyurethane, suffers from requiring a relatively long imagewise exposure time to adequately carry out the desired photoreaction in order to provide an exposed plate that is readily and effectively developable. An acceptable photospeed is important for all plates, including those having an exceptionally long run life, which is on the order of 250,000 impressions. Accordingly, there is a need for a photopolymer and a presensitized photopolymer plate coated therewith which exhibit acceptable photospeed when used in combination with a sensitizer such as a diazonium composition.
We have discovered that such a presensitized photopolymer plate is provided when the plate includes a photopolymeric composition having a polyurethane photopolymer with a polymeric backbone including recurring urethane and/or urea groups, which photopolymer has unsaturated hydrocarbon groups attached to the backbone. In an especially important aspect of this invention, the unsaturated hydrocarbon group is an allyl group, and the photopolymer is a polyurethane having pendant allyl groups attached to the polymeric backbone through an oxygen atom or ether linkage. In another important aspect of this invention, the photopolymer is in a solvent system, and its viscosity and molecular weight are controlled by reacting terminal --NCO groups of the polyurethane backbone with, if necessary, a diamine and/or a diol to chain extend and then a monoamine and/or a monoalcohol to provide a photopolymer that has substantially no terminal --NCO groups and that will not further chain extend to increase in viscosity and molecular weight.
It is accordingly a general object of this invention to provide a presensitized photopolymeric plate having an exceptionally long run life.
Another general object of the present invention is to provide, as a solution, a polyurethane photopolymer having reactive pendant groups and that has a selectable and controllable molecular weight and viscosity.
Another object of this invention is to provide an improved photopolymer which has a polyurethane backbone and, prior to photopolymerization, pendant groups that are especially reactive whereby the photopolymer is photopolymerized by actinic radiation of the type used for imagewise exposure of plates, including lithographic or planographic plates and photoresists such as those incorporated in the making of printed circuit boards and the like.
Another object of the present invention is to provide an improved presensitized photopolymeric plate that has adequate photospeed while possessing exceptional abrasion resistance by providing an exterior coating that is both tough and elastomeric.
Another object of the present invention is to provide an improved presensitized photopolymeric plate having a run life on the order of 250,000 copies or more.
These and other objects of the present invention will be apparent from the following detailed description of this invention.
Photopolymers according to this invention are generally classifiable as polyurethanes inasmuch as the backbone includes urethane groups and often also urea groups, which groups are recurring units within the polymer backbone. The photopolymer includes pendant or extra-linear reactive groups that depend from the backbone. As such, the photopolymer can be generally characterized as a polyurethane having pendant reactive groups. With more particular reference to the pendent reactive groups, such include unsaturated hydrocarbon moieties that are attached to the polyurethane backbone, preferably by means of an ether linkage.
The photopolymer according to this invention results from reacting a polyester, polyether, polyesteramide, polycaprolactone or polyacrylate module with an --NCO group of a diisocyanate compound and reacting an unsaturated ether compound with the other --NCO group of the diisocyanate compound. Typically, one of the -NCO groups reacts with an hydroxy group of the polymeric module, and the other --NCO group of the diisocyanate reacts with an hydroxy group of the unsaturated ether compound.
While plates according to this invention can be made from these photopolymers when they are prepared as polyurethane elastomers in a non-solvent system in accordance with United States Letters Pat. No. 3,043,807 and are subsequently coated from a solvent system, the photopolymers according to this invention are preferably prepared in a solvent environment. When the polyurethanes for providing plates according to this invention are prepared in a non-solvent system, such polyurethane elastomers, usually when in solid form, are put into solution with an appropriate solvent system for coating onto an appropriately treated or coated plate base.
In an especially important aspect of this invention, the photopolymer is prepared within a solvent system, most advantageously the solvent system from which the photopolymer will be coated onto the plate. In this regard, usually a prepolymer is first made and then added to a solvent system, unless the prepolymer itself had been prepared in a solvent system. Typically after chain extension by a diamine and/or a diol, a monoamine and/or a monoalcohol is then added to this prepolymer solution in order to permit reaction between the monoamine and free --NCO groups of the prepolymer in order to thereby substantially prevent further chain extension of the prepolymer backbone so that the molecular weight and viscosity of the resulting photopolymer solution is controlled at a selected level.
More particularly, the polyurethane photopolymer having unsaturated hydrocarbon groups attached to its backbone preferably is prepared by providing an hydroxy terminated module having the general formula HO--R--OH, wherein R is a polyester, a polyether, a polyesteramide, a polycaprolactone or a polyacrylate, this polymeric module being reacted with a diisocyanate of the general structure OCN--R'--NCO, wherein R' is a hydrocarbon that may include aromatic or non-aromatic structures, preferably aromatic structures. Such diisocyanate structure is further reacted with a dihydroxy compound having an unsaturated pendent group, whereby the isocyanate groups couple an hydroxy group of the polymeric module with an hydroxy group of the unsaturated dihydroxy compound. The dihydroxy compound having an unsaturated group has the general structure ##STR1## wherein R" is a non-aromatic or aromatic hydrocarbon. R"' is an unsaturated hydrocarbon of from about 2 to about 18 carbon atoms in length, and, when R" and the unsaturated hydrocarbon are to be joined together through an ether linkage, R"' is an unsaturated hydrocarbon of about 2 to 18 carbon atoms that has a terminal oxygen atom.
The resulting polymer, which has been found to be advantageously photopolymeric, includes a polyurethane backbone having recurring urethane groups, urea groups or combinations thereof and having spaced along the backbone and pendant to the backbone unsaturated hydrocarbon groups that are attached to the backbone. The spacing between the unsaturated ether pendant groups can be generally consistent if the polymer is made in a controlled manner, or the spacing can be varied if the polymer is formulated under random polymerization conditions. Generally speaking, the random polymerization will occur when the polyester type of or hydroxy-terminated polymeric module the diisocyanate and the unsaturated ether compound are generally simultaneously reacted together to form a prepolymer, while the structured type of polymer could be prepared by first reacting the hydroxy-terminated polymeric module with the diisocyanate in order to form an isocyanate-terminated prepolymer, after which the dihydroxy unsaturated compound would be joined to the free --NCO group of the isocyanate-terminated prepolymer.
It is important that the diisocyanate be added in excess when forming the prepolymer solution so that all of the hydroxyl groups of the polyester type of module and of the dihydroxy unsaturated compound react with the --NCO groups of the diisocyanate in order to form a polymer having a controlled molecular weight and having terminal --NCO groups.
Further regarding the addition of the amine and/or alcohol composition to the prepolymer in order to react with the terminal --NCO groups of the prepolymer, when desired, this addition can be a two-stage procedure, the first stage resulting in chain extension in order to increase the molecular weight and viscosity of the photopolymer to desired levels. Such chain extension will occur when the amine is a diamine and/or when the alcohol is a diol, which should be added very slowly in order to increase the viscosity and molecular weight as needed, at which time a monoamine and/or a monoalcohol is added as a second stage in order to react with and cap off the terminal --NCO groups to thereby prevent further chain extension by, for example, the presence of water within the polyurethane system.
In the hydroxy-terminated polymeric module, HO--R--OH, R is a polyester, a polyether, a polyesteramide, a polycaprolactone or a polyacrylate, and this polymeric module has terminal hydroxy groups as indicated by its formula. Each such hydroxyy-terminated polymeric module should have a molecular weight in the general range of between about 500 and about 7,000, typically between about 700 and 1,500.
The polyesters, containing hydroxyl groups, in the sense of the invention are, for example, reaction products of dihydric alcohols with dibasic carboxylic acids. Instead of the free dicarboxylic acids, the corresponding dicarboxylic acid anhydrides or corresponding dicarboxylic acid esters of lower alcohols or mixtures thereof can also be used for the preparation of polyester-polyols. The dicarboxylic acids can be of an aliphatic, cycloaliphatic, aromatic and/or heterocyclic nature and can optionally be substituted, for example by halogen atoms. Examples of these are: oxalic acid, malonic acid, succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, terephthalic acid, isophthalic acid, trimellitic acid, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, tetrachlorophthalic anhydride, endomethylenetetrahydrophthalic anhydride, glutaric anhydride, maleic acid, maleic anhydride, and fumaric acid. Dihydric alcohols which can be used, optionally mixed with one another, are, for example, ethylene glycol, propylene 1,2-glycol and propylene 1,3-glycol, butylene 1,4-glycol and butylene 1,3-glycol, hexane-1,6-diol, octane-1,8-diol, neopentylglycol, cyclohexanedimethanol, thiodiglycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycols, dibutylene glycol and polybutylene glycols. Exemplary preferred polyester-type modules of this type include poly(1,6-hexane adipate/isophthalate), poly(1,6-hexane/ adipate), the condensation product of adipic acid and ethylene glycol, and the condensation product of adipic acid, ethylene glycol and propylene glycol-1,2.
Polycaprolactones containing terminal hydroxyl groups, in the sense of the invention are, for example, included in those polyesters which are prepared by the polymerization of a lactone, for example of .epsilon.-caprolactone, or by the condensation of a hydroxycarboxylic acid, for example of .omega.-hydroxycaproic acid, with a starting material containing hydroxyl groups.
Representative polyether-type modules include polyethers made from ethylene oxides, propylene oxides, butylene oxides, tetrahydrofuran, and mixtures thereof. Representative polyacrylate-type modules include dihydroxy functional acrylic copolymers. Exemplary polyesteramides are made by replacing small amounts of the diols used in making the polyesters described herein with compounds such as ethanol amine, isopropanol amine, ethylene diamine, and 1,6-hexamethylene diamine.
Various diisocyanates that are suitable for use in preparation of the polymer according to this invention include the toluene diisocyanates such as 2,4-toluene diisocyanate and 2,6-toluene diisocyanate, 4,4'-tolidine diisocyanate, 4,4'-diphenylenemethane diisocyanate, 4,4'-cyclohexylmethane diisocyonate, 4,4'-diphenylmethane diisocyanate, m-phenylene diisocyanate, 4-chloro-1,3-phenylene diisocyanate, 4,4'-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,10-decamethylene diisocyanate, 1,4-cyclohexylene diisocyanate, 4,4'-methylene bis (cyclohexylisocyanate), 3,3'-dimethyl-4,4'-diphenylmethane diisocyanate and 1,5-tetrahydronaphthalene diisocyanate and mixtures of such diisocyanates.
Unsaturated dihydroxy compounds suitable for use in connection with this invention include glycerol-alpha-allyl ether, trimethylolpropane mono allyl ether, pentaerythritol diallyl ether, erytherol, glycerol-mono-allyl ether, allyl ethylene glycol, allyl propylene glycol, bis hydroxyethyl allyloxy succinate, vinyl cyclohexane diol, N,N-di(hydroxyethyl) allyl carbamate, dihydroxyethyl ether of 2-allyl hydroquinone; 2,2'-diallyl P,P' bisphenol.
Resulting polyurethane photopolymer solutions prepared by reacting these components have an unsaturated, pendant group for each molecular weight increment of between about 500 and 7,000 molecular weight. These polyurethane photopolymers have a total calculated molecular weight of on the order of approximately 50,000 to approximately 250,000 after addition, in solution, of the amine composition.
Plates according to this invention include a plate base or support member, which is typically a flexible sheet such as paper, metal, polymer film or the like, which has a surface having a layer and/or treatment that renders the plate base or support member more suitable for use as a plate, such as rendering it more hydrophilic. Coated thereover is a photosensitive system including one or mor layers of materials that are readily photopolymerizable or photolyzable in response to actinic radiation. In the preferred aspects of the present invention, such sensitizer system is a coating that includes a diazonium resin or condensate that is overcoated with the polyurethane photopolymer solution in accordance with this invention. Stabilizers and/or accelerators and other well-known components may be included within the sensitizer system in order to increase the shelf stability and/or to enhance the initial reactivity of the system to actinic radiation.
The present invention is especially suitable and finds particularly advantageous utility when the support member or plate base is anodized aluminum. In accordance with known techniques, an anodized aluminum plate base is brush grained or otherwise suitably treated to improve its ability to bond with a sub-base coating thereover and then washed to remove oils and contaminants which may be present on the surface thereof after such operations. Various sub-base coating materials are available, including phytic acid, melamine-formaldehyde resin condensates overcoated with polyacrylamide and thereafter treated with zirconium acetate. Other sub-base coatings include urea-formaldehyde, titanium orthoesters, silane-acrylics and silicate sub-bases such as those described in United States Letters Pat. No. 2,714,066. In addition, other sub-bases which are typically used on plates include gelatin, polyacrylic acid and water soluble salts thereof, polymethacrylic acid and water soluble salts thereof, carboxymethyl cellulose, carboxymethyl hydroxyethyl cellulose, certain titanates, modified resins of urea-formaldehyde and melamine-formaldehyde, polyvinyl alcohols, ferrocyanides, bichromates of sodium, potassium and ammonium, and oxides of the metal forming the plate, as well as combinations thereof and other sub-base materials.
Diazonium materials included within the sensitizing system according to this invention will typically be diazonium resins or diazonium condensates. Known diazonium materials include condensation products of an aldehyde with a diazonium compound having an amine substituent such as, for example, a water-soluble condensation product of para-diazo diphenyl amine and formaldehyde, these materials typically being furnished as salts, for example zinc chloride salts. Suitable is a diazonium mixed condensate prepared by condensing one mole of 3-methoxy-diphenylamine-4 -diazonium sulfate with one mole of 4,4'-bismethoxymethyl diphenylether in an 85% concentration of phosphoric acid which is isolated as mesitylene sulfonate.
Other diazo compounds which can be used include the diazo oxides such as pyrido [1 2-a]benzimidazol-8-y13 (4H)-diazo-4 (3H)-oxo-1-naphthalene sulfonate. Diazonium compounds which can also be used include such materials as
4'-bromo-diphenylamine-4-diazonium chloride; PA0 4'-chlorodiphenylamine-4-diazonium chloride; PA0 4-methoxydiphenylamine-4-diazonium chloride; PA0 3'-methoxydiphenylamine-4-diazonium chloride; PA0 3'-propoxy-diphenylamine-4-diazonium chloride; PA0 X,X.sub.1,X.sub.2 -tribromodiphenyl-amine-4-diazonium chloride; PA0 4'-methyldiphenylamine 4-diazonium chloride; PA0 4'-hydroxyldiphenylamine-4-diazonium chloride; PA0 4'-benzoylaminodiphenylamine-4-diazonium chloride; PA0 4'-fluoro-diphenylamine-4-diazonium chloride; PA0 2-anilidosulfonyldiphenyl-amine-4-diazonium chloride; PA0 2-(p-toluene-sulfonyl-amino)-diphenylamine-4-diazonium PA0 chloride; PA0 p-diazo-N-ethyl-N-benzyl aniline1/2 ZnC1.sub.2 ; PA0 4'-diazo-2-chloro-N,N'-diethylaniline-1/2 ZnC1.sub.2 ;
and other similar and well known diazonium materials.
The polyurethane photopolymer composition is typically laid down as a photosensitive overlayer on the diazonium resin coating, such polyurethane photopolymer being laid down from a solvent system in which the polyurethane photopolymer is included at a concentration of between approximately 0.005 weight percent up to about 5 weight percent. The bulk of the polyurethane photopolymer composition includes one or more solvents such as toluene, cyclohexanone, xylene, isopropanol, ethyl acetate, methyl ether ketone, diglyme (diethylene glycol dimethyl ether), ethyl diglyme, and the like. Photoaccelerators, pigments, oxidation retardants and photochromic dyes may be included as desired in order to enhance the ability of the photopolymer to absorb actinic energy and photoreact.